In an LTE system, carrier aggregation (CA: carrier aggregation) for performing communication by simultaneously using a plurality of carries is adopted, in which a predetermined bandwidth (20 MHz at the maximum) is used as a basic unit. In carrier aggregation, a carrier which is a basic unit is called a component carrier (CC: component carrier).
When CA is performed, a PCell (Primary cell) that is a reliable cell for ensuring connectivity and an SCell (Secondary cell) that is an appendant cell are set for the user apparatus UE. The user apparatus UE connects to a PCell first, and then, an SCell can be added as necessary. The PCell is a cell similar to an independent cell supporting RLM (Radio Link Monitoring) and SPS (Semi-Persistent Scheduling) and the like.
The SCell is a cell which is set in the user apparatus UE by being added to the PCell. Addition and deletion of an SCell can be performed by RRC (Radio Resource Control) signaling. Since SCell is in an deactivated state right after it is set in the user apparatus UE, communication becomes available (scheduling becomes available) only by activating it.
As shown in FIG. 1, in CA up to Rel-10 of LTE, a plurality of CCs under the same base station eNB are used.
On the other hand, in Rel-12, this is further expanded so that Dual connectivity is proposed in which simultaneous communication is performed by using CCs under different base stations eNB to realize high throughputs (non-patent document 1). That is, in Dual connectivity, the UE performs communication simultaneously using radio resources of two physically different base stations eNB.
Dual connectivity is a kind of CA, and it is also referred to as Inter eNB CA (inter-base station carrier aggregation), in which Master-eNB (MeNB) and Secondary-eNB (SeNB) are introduced. FIG. 2 shows an example of Dual connectivity. In the example of FIG. 2, an MeNB communicates with the user apparatus UE by a CC#1, and the SeNB communicates with the user apparatus UE by a CC#2 so that Dual connectivity (to be referred to as DC hereinafter) is realized.
In DC, a cell group formed by cell(s) (one or a plurality of cells) under an MeNB is called MCG (Master Cell Group), and a cell group formed by cell(s) (one or a plurality of cells) under an SeNB is called SCG (Secondary Cell Group). An UL CC is set in at least one SCell in an SCG, and PUCCH is set in one of the at least one SCell. The SCell is called PSCell (primary SCell). An SCell added first in an SCG is the PSCell. Note that it is being considered, in also CA which is not DC, to set a PUCCH in an SCell.
By the way, in LTE, for the purpose of reducing power consumption in the user apparatus UE, DRX (Discontinuous reception) is defined (non-patent document 2). In DRX, as shown in FIGS. 3A and 3B, the state changes from a non-DRX state for always trying reception of a signal (PDCCH) to a DRX state for periodically performing discontinuous reception of a signal when there is no communication for a predetermined time. Configuration information (configuration) of cycle, reception period and the like related to DRX is notified from the base station eNB to the user apparatus UE by an RRC signal and the like.
In communication of a single carrier which is not CA and in CA up to Rel-10, the base station eNB performs single DRX configuration for the user apparatus. On the other hand, in the above-mentioned Dual Connectivity, the MeNB and the SeNB can perform DRX configuration for the user apparatus UE independently. That is, DRX configurations that are different between the MeNB and the SeNB can be made, so that the user apparatus UE manages states of DRX independently for each of them. That is, in the user apparatus UE, a DRX state and a non-DRX state can be taken at the same time.
On the other hand, in LTE, it is defined that the user apparatus UE measures quality (RSRP, RSRQ and the like) of serving cells and neighbor cells to report the quality to the base station eNB in terms of cell selection processing at the time of handover, and CC addition/deletion/change processing in CA/DC. This is called measurement.
As to measurement, in LTE, as measurement conditions (requirements), allowable time until measurement completes and the like are specified (non-patent document 3). In the specification, different measurement conditions are specified depending on whether the user apparatus UE is in a DRX state or in a non-DRX state. Also, a measurement condition that should be satisfied when in DRX is specified depending on a cycle of DRX (to be referred to as DRX cycle hereinafter).